1. Field of the Invention
The invention relates to a developing apparatus which is typically utilized in an image forming device such as a copying machine, facsimile machine, printer, etc. In particular, the present invention provides an improved developing apparatus and method, particularly with regard to the supply or carrying of developer by a developing roller which supplies developer to a latent image carrying body such as a photosensitive element. Significantly, an improved developer carrying roller is provided which supplies one-component developer to the photosensitive element.
2. Discussion of Background
Recently, a large number of developing devices have been designed and used which employ one-component developer in order to simplify the developing device and reduce the cost thereof. One-component developer does not contain a carrier (which functions as a developing electrode in the developing area and facilitates carrying of toner). For carrying one-component developer, a dielectric layer is formed on the surface of the developer carrying body, such as a developer carrying roller. In order to improve image quality, the surface of the roller can be roughened utilizing a sandblasting or sandpapering technique, thus improving the carrying force for the developer. Alternatively, the developer carrying body's surface can be provided with a concave/convex surface to allow the surface to function as an electrode.
Japanese Laid-Open Patent Publication No. 55-153973/1983 provides an example of a developer carrying body which is formed of a smooth concave/convex surface, with the objective to enable stable formation of images over a long period of use. Japanese Laid-Open Patent Publication No. 55-113070/1980 describes the surface of a developer carrying body of a contact developing type which is formed of a resilient material having a surface roughness which is not smaller than 6 .mu.m. Further, Japanese Laid-Open Patent Publication No. 59-126567/1984 teaches the roughness of the developer carrying body can be formed in the range 2-10 .mu.m utilizing sandblasting or sandpaper. Further, Japanese Laid-Open Patent Publication No. 59-189374/1984 teaches that a non-contact type developing device for use with nonmagnetic toner can be provided with a surface having peaks or protrusions which are 2.75-3.0 times the average particle diameter of the developer to be used. Further, the distance between the adjacent peaks should be made larger than the height of each peak, and smaller than the development gap (i.e., the distance between the surface of the photosensitive body and the developer carrying body).
A further example of the various types of developer carrying bodies or rollers is provided in Japanese Laid-Open Publication No. 3-4461/1991 in which the developing apparatus includes a sleeve-shaped developer carrying body having a surface roughness of 2-3 times the average particle diameter of the developer, with a scraper provided for scraping off any remaining toner adhering to the developer carrying body. Japanese Laid-Open Publication Nos. 3-1419/1991 and 3-14192/1991 respectively describe an alumite treatment is provided upon the surface of the one-component developer carrying body, and thereafter the smoothness of the developer carrying body's surface is roughened by sandblasting using fixed form or non-fixed form particles. However, when utilizing a developer carrying body having a dielectric surface layer and a contact type developing method, it has been recognized that projecting portions of several .mu.m cause a concentration of the electric field on the surface of the dielectric body, which results in an abnormal image. Often such an image will have a blank area. To avoid this problem it has been necessary to suppress the roughness of the dielectric area to less than 5 .mu.m.
However, when the surface of the dielectric layer is smooth, additional problems results in that charging of the developer can be insufficient (for example, as in the arrangement of Japanese Laid-Open Publication No. 59-126567/1984), and the developer carrying ability is weakened. In addition an overdeveloping phenomenon (fogging) on background areas of an image often occurs. Further, problems can be encountered with the formation of lines which are parallel to the direction of movement of the latent image carrying body, with such lines developed thinly, and in some instances the developed line will be broken-off or include a discontinuity (this problem is referred hereinafter as thin longitudinal line development or longitudinal line thinning).
Accordingly, an improved developing apparatus and method is desired which can avoid the foregoing problems. In particular, a developing unit and process for one-component developer is desired which avoids problems associated with fogging and thin line longitudinal development. Such an arrangement, or process should also avoid problems associated with previous roughening approaches, e.g., abnormal or blank areas resulting from concentrations in the electric field. In addition, such a developing apparatus should have a relatively simple construction, thereby avoiding increased costs of manufacture.